This invention relates to a sliding seal which comprises a profiled flexible base member and within the sliding zone a layer of material having a low coefficient of friction, wherein the layer is extended beyond the sliding zone and is connected with the base member in a shear-resistant manner outside of the friction zone. This invention is related to and is an improvement of the sliding seal construction disclosed in copending, commonly owned U.S. patent application Ser. No. 538,265, filed Jan. 3, 1975. The contents of said copending application are hereby incorporated by reference thereto herein, insofar as such will aid in an understanding of the subject matter of the present invention.
The principle on which this invention is based resides in that the layer present in the sliding zone, made of a material having a low coefficient of friction, which is to effect a reduction in the friction force, is not firmly joined to the base member in the sliding or friction zone -- as is the case in the sliding seals known heretofore -- but rather is extended past the sliding zone and is joined to the flexible base member only outside of this sliding zone either directly or by way of a connecting element.
This astonishingly simple measure results in a sliding seal with surprising advantages, especially (but not exclusively) during its manufacture, installation, and utilization.
Thus, it is now no longer necessary, when utilizing this invention, to apply or mount layers with maximum firmness to a flexible base member with the aid of complicated processes or expensive methods; rather, it is possible to use, quite simply, a sliding layer, e.g. a film, a band, or a profile, brought together with the base member so that in case of a frictional engagement, this layer shields or covers the base member within the sliding zone.
Thus, the essential aspect in this connection is that only in case of a frictional engagement is the layer pressed against the base member, or vice versa. It is thereby made possible to make the base member essentially responsible alone for the pressure contact of the sliding layer with the moving counter member and thus for the sealing action, and to design the base member with respect to its configuration optimally for this sealing effect. In contrast thereto, the sliding layer made of a material of a low coefficient of friction is solely responsible for attaining low coefficients of friction, wherein the thus-occurring friction forces are absorbed by this layer and are transmitted outside of the sliding zone to the mounting points of this layer to the support member and are transferred to the latter. As a result, a complete separation of the structural elements responsible for the sealing function and for the sliding function has been achieved, making it possible to design these components optimally for the respective, specific task.
Additional advantages of this sliding seal, preferably executed constructional measures, as well as particularly suitable materials have been described in detail in the above-identified application and are equally advantageously applicable to the arrangement of the present invention as described hereinbelow.
The preferred arrangements of the sliding seal according to the above-identified application do satisfy the posed requirements in the fields of application recited in said application to a high degree: thus, they take care, in any event in a specific relative friction and sliding direction, respectively, of an excellent sealing action due to the tongue-like overlapping of the base member by the layer. However, if there is a reversal of motion during the sliding step, it may happen, however, when certain unfavorable conditions prevail that the sealing effect of these sliding seals is somewhat impaired, namely if the sliding layer should be pulled off the base member due to adverse conditions, and the base member than comes into undesirable contact with the moving sliding member.
However, there are cases of utilizing the sliding seals wherein constantly changing sliding directions occur, or even sliding functions occur in all directions, and wherein a sufficient sealing effect must always be ensured, for example during use as a continuous shaft seal in marine engines. Starting with this consideration, the present invention is based at least in part on the task of developing and improving the subject matter of the above-identified application so that even in case of a reversal of motion of the sliding movement, in case of a change in the direction of movement, or even in case of any desired motion direction, the required sealing function of the seal is reliably ensured.
This problem is solved in accordance with the invention by providing that the base member has a profiled support member fully covered by the layer, which latter is joined on both sides of the support member with the base member. Although the layer has a low coefficient of friction with respect to the edge to be sealed and being moved relatively thereto, it has heretofore been impossible to entirely prevent, under especially adverse conditions, that the layer was pulled off the base member when the direction of movement was changed. Such conditions occur, for instance, if foreign bodies or especially tacky deposits contaminate the sealing zone. In this case, the joining of the layer with the base member on both sides of the support member according to this invention provides that the layer is capable of absorbing tensile stresses. These tensile stresses are produced, on the one hand, by the contact force of the support member effective in the sealing direction and, on the other hand, by the effect of foreign impurities effective, for example, on the sliding layer in the sealing zone during a movement of the surface to be sealed. The sealing zone herein is merely the coherent surface, within which the support member applies a force on the counter surface to be sealed by way of the layer.
Furthermore, the invention affords the further advantage that the support member is surrounded on all sides by a layer protecting the support member, which layer is either the sliding layer by itself or in conjunction with the base member. Consequently, the support member is not only exposed to a lesser extent to the mechanical effect of foreign bodies than has previously been the case, but is not exposed either to other influences as much as heretofore, such as, for example, to light, an agressive atmosphere, etc., since the covering layer offers protection. Accordingly, it is also possible to install the seal of the present invention, for example, in windows in any desired orientation, since there is no longer any need for differentiating between a weather side and an interior side. This leads to a considerable simplification of the installation of the sealing strip according to this invention.
The basic function of the support member resides in supplying the contact force necessary for sealing purposes, wherein a distribution of the contact force is to be attempted which is maximally uniform over the entire sealing zone, in order to attain a uniform sealing action. It is contemplated, for example, to employ as the support member according to preferred embodiments of the invention, a tightly coiled spiral spring of a thin, resilient spring wire. In this connection, it is especially advantageous to provide the individual turns of the spiral spring so closely together that the desired uniform contact force is ensured along the sealing zone if the forces introduced by the individual spring wires are distributed by the layer extending over the support member. However, in other especially preferred embodiments of the invention, a support member is advantageously utilized of a foamed synthetic resin or of an essentially homogeneous, e.g. elastomeric material, the uniform contact force of which results from a compression thereof. Also the elastomeric sealing member may according to the invention, depending on the purpose for which it is used, exhibit a plurality of shapes which are of particular advantage in a respective instance, for example the configuration of a tube extending along the sealing zone, or a solid, round material. This provides the advantage that a string-like material manufactured by mass production techniques can be utilized for the support member which need not even be separately attached to the sealing strip of this invention, since it is already held adequately by the layer joined on both sides to the base member. Such arrangements have special advantage where a relatively small sealing play is to be expected. However, where a large amount of sealing clearance can occur, a support member is necessary or contemplated by the invention which is capable of yielding a sufficient contact force over a wide sealing clearance without such force becoming unduly high and thus leading to wear or the development of heat in case of a particularly small seal spacing. Accordingly, an especially advantageous embodiment of the invention resides in fashioning the support member as a backing (supporting) lip. The height of this backing lip is, in a particularly advantageous embodiment, essentially larger than the largest amount of sealing play to be expected. If the sealing play is amller than the height of the sealing lip, then the latter will arch in the direction of movement of the surface to be sealed in the proximity of the sealing zone and will contact the latter, since as is known a lip is an element having a cross section which is reduced in the upward direction. Thus, ensurance is obtained that the arched-over supporting lip is constantly in engagement with the sliding layer which latter, in turn, is in constant engagement, in the friction zone, with the counter surface to be sealed, on account of the contact forces resulting from the effect of the backing lip.
The invention, under certain circumstances, advantageously provides that the support member and/or the backing lip are in constant contact with the layer, even if the sealing strip of this invention is not in engagement with a counter surface to be sealed. This is of advantage particularly if a single sealing strip is utilized to seal several, differently moved counter surfaces, since in such a case there could be the danger that, with surfaces to be sealed which have different directions of motion, the supporting lip, as seen along the sealing strip, would be bent once toward one side and then toward the other side, producing an intermediate zone of increased stress in the supporting lip.
According to a further embodiment of the invention, however, it is of special advantage to have the layer in contact with the support member and/or the backing lip only in case of a sealing engagement in the friction zone. If the sealing strip according to this embodiment is not in sealing engagement, the sliding layer curves away from the base member so that the support member and/or the backing lip are freed. Accordingly, the support member and/or the backing lip can be reoriented with each new sealing engagement with a respective counter surface in such a way that by the bending of the support member and/or the backing lip in the direction of movement of the counter surface to be sealed, the particular advantages provided by the sealing strip of this invention are in each case maintained. Moreover, the additional advantage is achieved that the sealing strip of this embodiment according to the invention provides a sealing effect even if the tolerance range in the spacing between the sealing strip and the counter surface to be sealed exceeds the possible spring deflection (stroke) of the support member, since due to the arching of the layer the latter still remains in engagement with the counter surface to be sealed.
This is of advantage particularly in case of shaft seals wherein, when passing through critical speed ranges, an especially high sealing clearance occurs for short periods of time.
To prop up the sliding layer, it is contemplated to employ a layer having a certain inherent resiliency characteristic. However, according to a further embodiment of the invention, it is especially advantageous to fill the space between the layer, on the one hand, and the base member, on the other hand, with a gas having a higher pressure than the pressure ambient outside of the sliding seal. In this embodiment, the spring effect of the support member is supported and/or the lifting off of the layer is ensured, by the compression of the occluded gas cushion. By the excess-pressure filling according to this invention, it is, however, also made possible to prevent any medium to be sealed off by way of the junction zones between the layer and the base member from leaking out by circumventing the sliding seal of this invention. Depending on the material employed for the support member, an inert gas particularly harmless to the support member can be utilized for the gas filling. This does not only prevent the oxidation of the support member, but rather this arrangement is also of special advantage in cases where a gas must be sealed off which is particularly aggressive to the support member.
Preferably, the sliding layer is chosen to be of such a length and is mounted outside of the friction zone to the base member in such a way that it projects therefrom except at the mounting points, and contacts the base member only under sealing engagement at least in the friction zone. Preferably, the sliding seal of this invention is attached by means of its base member; applications are definitely contemplated wherein this base member is not flexible, such as for example the support member, but rather is made preferably of an inelastic or even rigid material, e.g. a metal, a hard synthetic resin, or also of cardboard. It can, however, also be advantageous to make the base member elastic, for example to be able to press same especially conveniently into a preformed groove. In this connection, it is particularly advantageous according to other preferred embodiments to fashion the base and support members and/or the backing lip in one piece as an integral cord (spring, skein).
Due to the sliding seal according to this invention consisting of a base member, a covering sliding layer, and a support member, it is now no longer troublesome if the seal formed thereby is engaged, somewhat entrained, or bent over by the counter surfaces to be sealed which is moved relatively thereto. The invention ensures that in any event the sliding layer continues to remain in contact with the base member in the sliding zone. Even if foreign bodies are forced to move through the friction zone by the counter surface to be sealed, this does not prevent the reestablishment of a full seal by the sliding seal of this invention after the foreign body has passed through, as long as this seal has not been damaged mechanically. In particular, there is no danger that the sliding layer will perhaps be lifted off the support member, and the support member and the counter surface to be sealed come into undesired contact with each other.
According to preferred embodiments of the invention, the base member and the layer are in contact with each other, but this does not mean that the layer must be directly attached to the base member; rather, it is also contemplated for the layer to introduce its forces into the base member by way of connecting members. An important aspect of the invention is that the forces are not transmitted from the layer into the support member in the sliding zone, and thus damage the support member proper.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.